High temperature gas furnace

ABSTRACT

A circulation heater for heating to a high temperature gas under high pressure. The furnace includes an inner container and an outer container with gas pervious insulation positioned between the two containers. Electric heating elements extend into the inner container for heating gas received in the inner container. The inner container has openings, including openings around the electric heaters so that the insulation between the containers is in communication with the gas in the inner container. In the preferred embodiment, the insulation between the side walls of the containers is in the form of an insulation insert: including radially inner and outer walls with insulation held between the walls. The inner wall is shorter than the outer wall and the insulation to provide a communication path for the gas to the insulation. The insulation between adjacent walls at one end of the containers may be in the form of a plug of porous insulation brick which serves the dual purpose of providing insulation and physically supporting the inner container.

Skogland United States Patent [1 1 1 HIGH TEMPERATURE GAS FURNACE [75]Inventor: Thorbjorn Skogland, Shelbyville,

[73] Assignee: General Electric Company,

Indianapolis, Ind.

22] Filed: Sept. 27, 1973 211 Appl. No.: 401,250

219/381. 390, 400, 401,408, 406; 126/110 R, 91 A, 99 A, 116 C; 137/341[56] I References Cited UNITED STATES PATENTS 1,540,401 6/1925 Kelly etul 219/406 1,946,262 2/1934 Adams 219/379 1,949.658 3/1934 Remseth et111.... 219/380 1,985,280 12/1934 Carleton 219/380 2,462,746 2/1949lnman 219/379 2,711,473 6/1955 Mahaffy et al.. 137/34] 2,768,277 10/1956Bucket a1 13/20 X 2,836,696 5/1958 Ratchford t 219/390 3,109,912 11/1963Cerulli ..2l9/381 3,226,467 12/1965 Kienel et a1 219/400 X l W f Mar.25, 1975 3,383,495 5/1968 Laube et a1 219/380 X PrimaryExaminer-Volodymyr Y. Mayewsky [57] ABSTRACT A circulation heater forheating to a high temperature gas under high pressure. The furnaceincludes an inner container and an outer container'with gas perviousinsulation positioned between the two containers. Electric heatingelements extend into the inner container for heating gas received in theinner container. The inner container has openings, including openingsaround the electric heaters so that the insulation between thecontainers is in communication with the gas in the inner container.

in the preferred embodiment, the insulation between the side walls ofthe containers is in the form of an insulation insert: includingradially inner and outer walls with insulation held between the walls.The inner wall is shorter than the outer wall and the insulation toprovide a communication path for the gas to the insulation. Theinsulation between adjacent walls at one end of the containers may be inthe form of a plug of porous insulation brick which serves the dualpurpose of providing insulation and physically supporting the innercontainer.

3 Claims, 3 Drawing Figures PATENTEBHARZSIBYS SHEET 1 [IF 2 BACKGROUNDOF THE INVENTION The presentinvention relates to furnaces for heatinggas and, more particularly, to circulation heaters for heating to hightemperatures gasesunder' high pressure.

It often is desired to heat various gases to high temperatures. Theproblems involved in furnaces for this purpose become much morecomplicated when the gas being heated is under high pressure. Thestrength of materials used in constructing gas furnaces lessens as theirtemperature is increased. Therefore, the furnace walls must be muchthicker to withstand the pressure at high temperature. By way ofexample, a typical furnace material may be a Grade 332 stainless steelwhich is a high nickel, high chromium content stainless steel. A 3 inchthick plate of this material at 350 Farenheit will successfullywithstand a pressure in the range of I75 pounds per square inch.However, if the temperature of the material is raised to 1700 Farenheit,the plate would have to be over 20 inches thick in order to successfullywithstand a pressure of 175 pounds per square inch.

Because of the combined temperature-pressure effect it is very difficultto construct furnaces for heating high pressure gases to hightemperatures which have reasonable size and cost relative to the volumeof gas to be heated.

SUMMARY OF THE INVENTION It is therefore an object of the presentinvention to provide an improved furnace.

Another object of the invention is to provide such an improved furnaceparticularly adapted for heating to high temperatures gas under highpressure.

Yet another object of the present invention is to provide such animproved furnace which makes economic use of material used inconstruction of the furnace.

Yet another object of the invention is to provide a hightemperature-high pressure gas circulation heater having an optimum sizefor the volume of gas to be heated.

The present invention, in accordance with one embodiment thereof,provides a gas furnace which includes an outer container and an innercontainer for receiving gas to be heated. Heating means is provided forheating gas received in the inner container. The inner container ismounted within the outer container in spaced relationship thereto andgas pervious insulation is positioned between the inner and outercontainers so that the operating temperature of the outer container issubstantially lower than the operating temperature of the innercontainer. The inner container has at least one opening communicatingwith the gas pervious insulation so that the inner container issubjected to a low pressure differential.

The above mentioned and other features and objects of this invention, aswell as one manner of obtaining them, will become more apparent and theinvention itself will be better understood by reference to the followingdescription of a preferred embodiment of the invention taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a somewhat simplified andschematic plan view ofa furnace incorporating one form of the presentinvention.

FIG. 2 is a cross-sectional view of the furnace of FIG. 1, as seen alonga longitudinal axis of the furnace.

FIG. 3 is an enlarged, fragmentary view as taken along 3-3 in FIG. 1,showing certain details of construction of one of the conduits utilizedin providing gas to the inner container.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings,and particularly to FIGS. 1 and 2, there is shown, in somewhat schematicform, a furnace or circulation heater particularly adapted to heat to ahigh temperature gas which is under a high pressure. The furnaceincludes an inner container 11 and an outer container 12. The innercontainer 11 conveniently may be cylindrical in shape having end walls13 and 14 joined by a generally cylindrical side wall 15 by somesuitable means such as weldmg.

The outer container 12 also is cylindrical in shape having end walls 16and l7joined by generally cylindrical side wall 18. Conveniently the endwall 17 and side wall 18 may be welded together as indicated at 19 whilethe end wall 16 is removably connected to side wall 18. To this end, acollar 20 is welded around the upper end of the side wall 18. The endwall 16 is attached to the collar 20 by a number of bolts and nuts suchas those shown at 21 and 22 with a gasket 23 sandwiched therebetween.With this arrangement, the end wall 16 may be removed to provide accessto the interior of the furnace.

The inner container 11 is substantially smaller than the outer container12 and is mounted within the outer container in spaced relationshipthereto. To this end, a plug 24 of porous insulation brick material ispositioned between the end walls 14 and 17. The furnace normally ismounted with the end walls 14 and 17 positioned downwardly. The plug 24serves dual purposes of insulating the wall 17 from the wall 14 andproviding physical support for the inner container 11. Conveniently theplug may be made of a aluminum silicate.

The annular space between side walls 15 and 18 is filled by aninsulating insert including an outer cylindrical wall 25 and an innercylindrical wall 26 which sandwich a body 27 of fibrous insulationmaterial between them. The outer wall 25 fits snugly along the innersur-' face of wall 18 while the inner wall 26 is spaced slightlyoutwardly of the wall 15. The wall 25 extends the full distance from theplug 24 to the gasket 23 as does the body 27 of insulating material. Thewall 26, however, is shorter than the wall 25 and is positioned so as tostop above the insulating plug 24. This exposes the lower portion ofinsulation body 27 to inner container 11.

A collar 28 is attached to the inside of wall 26 in a position spacedsomewhat above the end wall 13 of the inner container and supports aplate 29. The space between the plate 29 and theupper end wall 16 of theouter container is filled with insulating material generally indicatedat 30. Conveniently, the bodies 27 and 30 of insulating material may becomposed of the same 3 material and conveniently may be of aluminumsilicate fiber.

Gas received in the inner container 11 is heated by means of elongatedelectrical heating elements such as those indicated at 31. Each of theheating elements is generally U-shaped in con-figurationand extends froma terminal box 32 through the end wall 16, insulation 30, plate 29 andend wall 13 into the inner container 11. The openings in the end wall 16fit tightly about the heating elements 31. In fact the heating elementsmay be welded to the end plate 16 as indicated at 33. Contrary to this,the openings 34 through plate 29 and the openings 35 through the endwall 13 are larger than the heating element 31.

In order to provide for the passage of gas through the inner container11, so that it may be heated by the heating elements 31, the furnaceincludes a pair of conduits generally indicated at 36 and 37. Theconduit 36 conveniently may be provided at the end of the furnaceopposite the terminal box 32. The conduit 36 includes a pipe 38 whichextends from the interior of container 11 through an opening 39 in endwall 14, an opening 40 in the insulation plug 24 and an opening 41 inthe end wall 17 to the exterior of the outer container. The openings 39and 40 are only slightly larger than the outside diameter of the pipe 38while the opening 41 is substantially larger. The opening 41 is filledwith insulation material 42 which extends beyond end plate 17 and alsofills a short pipe 43. One end of the pipe 43 is welded to the outsideof end plate 17 while the other end of pipe 43 is welded to one end ofasmaller diameter pipe 44 which fits tightly about pipe 38. The other endof the pipe 44 is welded to the outer end, of pipe 38 and to a collargenerally indicated at 45. The various weld connections between thepipes and collar provide gas tight seals so that no gas may leak fromthe outer container 12 even though it leaks from the inner container.With this arrangement, the pipe 38 is firmly held into position in thelower portion of the container 12. lt is desirable that the outersurfaces of the furnace be at somewhat lower temperatures than the hightemperature to which the gas isheated. A coil 46a is positioned aroundpipe 43 and is connected to a suitable cooling unit, not shown, so as tomaintain the exposed portions of conduit 36 relatively cool even thoughthe gas flowing through the pipe 38 is at a very high temperature.

Additional details of the conduit 37 are shown in FIG. 3 and are quitesimilar to the conduit 36. The conduit 37 includes a pipe 47 whichextends from the interior ofinner container 11 through an opening 48 inside wall and then through the insulation insert, including walls 25 and26 and insulation material 27, and the cyclindrical wall 18 of the outercontainer 12. Another pipe 49 fits in the opening in outer wall 18around the pipe 47 and is welded to the wall 18. The space between thepipes 47 and 49 is filled with insulation material 50. Another pipe 51fits tightly about the pipe 47 beyond the pipe 49 and is welded to thepipe 49. A collar 52 fits around the pipe 51 and is welded to it. Theouter end of pipe 47 is formed as an outwardly extending flange 47a andfits within the opening of the collar 52. When another device or conduitis attached to the collar 52 a gas tight seal is formed at the outer endof the pipe 47. With this arrangement the pipe 47 may be pulled out ofthe furnace sufficiently to allow the insulation insert including walls25 and 26 and insulation 4 material 27 to be removed from the furnaceaxially. A coil 46b is positioned about pipe 49 and may be connected tothe same coolingsource as coil 46a.

A pair of purgeoutlets generally indicated at 53 and 54 are provided atthe axially opposite ends of the outer container. These purge outletsenable the air between the inner and outer containers to be evacuatedand replaced with a suitable gas such as nitrogen prior to operation ofthe furnace.

In operation the gas to be heated is admitted to the inner containerthrough conduit 37 and is heated by the heating elements 31. The heatedgas exits through the other conduit 36. Thisgas may be at a very hightemperature and pressure. By way of example, in one application, amixture of methane, carbon monoxide and hydrogen has a furnace entrancetemperature of approximately 1300 Farenheit and a furnace exittemperature of about l700 Farenheit as it leaves the furnace. The gas isunder a pressure of pounds per square inch. Asingle wall furnace toserve this purpose constructed of a high grade stainless steel wouldrequire extremely thick walls, particularly the end walls.

By means of the present invention, it is possible to greatly reduce thesize of the walls. This provides savings in both material and space. Aspreviously described, the openings 35 in the end wall 13 of the innercontainer are larger than the heating elements and the opening 39 aboutpipe 38 is larger than the pipe 38. Also as previously described, thewall 26 is spaced from the wall 15 and terminates above the insulationplug 24. Additionally, the openings 34 in plate 29 is larger than theheating elements 31. With this arrangement, the space and thus theinsulation, between the containers is in gas communication with theinterior of the inner container 11. Additionally, all of the insulationis gas pervious. Therefore. if the gas within the inner container 11 isat 175 PS1, by way of example. then the pressure in the area between theinner-and outer containers will also be approximately 175 PS1. Thismeans that the inner container is required to withstand little or nopressure differential.

Since the temperatures and pressures within the furnace will quicklyreach an equilibrium there is little or no gas flow through theinsulation from one portion of the inner container to another portion ofthe inner container and therefore there is no conviction heat transferto the various portions of the insulation. This means that, even thoughthe pressure present in the insulation is quite high, its insulationcharacteristics are not adversely affected and the insulation iseffective to maintain the temperature of the outer container, includingend walls 16 and 17 and side wall 18, at a much lower temperature. Forinstance, in the application described briefly above, the outsidesurface temperature of the outer container is maintained at about 350.

With this arrangement, the inner container 11, which is subjected to anextremely high temperature, is subjected to little or no pressuredifferential and may be constructed of thin material. On the other handwhile the outer container is subjected to a high pressure itstemperature is maintained at a much lower level than the inner containerand it also may be constructed of thin material.

While in accordance with the patent statutes, 1 have described what, atpresent, is considered to be the preferred embodiment of my invention,it will be obvious to those skilled in the art that numerous changes andmodifications may be made therein without departing from the invention,and it is therefore claimed in the appended claims to cover allequivalent variations as fall within the true scope and spirit of theinvention, What I claim is new and desire to secure by Letters Patent inthe United States is:

1. A furnace for heating gas, including: an elongated, generallycyclindrical inner container for receiving gas to be heated; heatingmeans extending into said inner container for heating gas therein;conduit means communicating with said inner container for supplying gasto said inner container and for removing gas from said inner containerafter the gas has been heated; an elongated, generally cyclindrical, gastight outer pressure container positioned around said inner container inspaced relationship thereto; gas pervious insulation substantiallyfilling the space between said inner and said outer containers so thatthe operating temperature of said outer container is substantially lowerthan the operating temperature of said inner container; said insulationincluding an insulation insert removably received between the side wallsof said inner and outer containers; said insert including coaxial,radially spaced apart cyclindrical members separated by a body ofgaspervious insulation; the inner of said members being spaced outwardly ofthe side wall of said inner container and axially shorter than said bodyof gas pervious insulation so that said body of gas pervious insulationis in communication with said inner container; and

said inner container having at least one opening communicating with saidinsulation so that said inner container is subjected to no more than alow pressure differential.

2. A furnace as set forth in claim 1, wherein: said heating meansincludes at least one electric heating element extending through onewall of said inner container; said one wall of said inner containerbeing spaced from said at least one heating element,

3. A furnace as set forth in claim 1 wherein; said inner and outercontainers include spaced apart end walls and a brick plug of porousinsulation material is positioned between corresponding end walls ofsaid inner and outer containers.

1. A furnace for heating gas, including: an elongated, generallycyclindrical inner container for receiving gas to be heated; heatingmeans extending into said inner container for heating gas therein;conduit means communicating with said inner container for supplying gasto said inner container and for removing gas from said inner containerafter the gas has been heated; an elongated, generally cyclindrical, gastight outer pressure container positioned around said inner container inspaced relationship thereto; gas pervious insulation substantiallyfilling the space between said inner and said outer containers so thatthe operating temperature of said outer container is substantially lowerthan the operating temperature of said inner container; said insulationincluding an insulation insert removably received between the side wallsof said inner and outer containers; said insert including coaxial,radially spaced apart cyclindrical members separated by a body of gaspervious insulation; the inner of said members being spaced outwardly ofthe side wall of said inner container and axially shorter than said bodyof gas pervious insulation so that said body of gas pervious insulationis in communication with said inner container; and said inner containerhaving at least one opening communicating with said insulation so thatsaid inner container is subjected to no more than a low pressuredifferential.
 2. A furnace as set forth in claim 1, wherein: saidheating means includes at least one electric heating element extendingthrough one wall of said inner container; said one wall of said innercontainer being spaced from said at least one heating element.
 3. Afurnace as set forth in claim 1 wherein; said inner and outer containersinclude spaced apart end walls and a brick plug of porous insulationmaterial is positioned between corresponding end walls of said inner andouter containers.